Once upon a time, in a land, far, far away, there were two mobile operating systems. One of them was designed for mobile from the ground up; the other was trying really hard to copy its older, desktop brother. One was limited in functionality, inflexible and lacked multitasking, but was very efficient, fast, and easy to use. The other had everything and the kitchen sink, was very flexible and could multitask, but had a steep learning curve, was inconsistent, and not particularly pretty.

Yeah, that stands to reason since K-9 Mail is based on the stock client's source, and their ultimate goal is to push their improvements back upstream so that everyone has access to stuff like PGP/GPG encryption in their stock client. K-9 Mail is so good, in fact, that it even worked fine on cwhuang's horribly unstable Honeycomb x86 builds.